The present invention relates to sulfur abatement. The present invention further relates to methods to remove sulfur or sulfur-containing species from various sources, such as a gas stream or liquid stream.
In many applications, it is desirable to reduce the level of gaseous sulfur compounds such as H2S, COS, mercaptans, etc. Many applications, e.g., fuel cells, require that the gaseous sulfur compounds in a raw fuel stream (e.g., naphtha, LPG, town gas, etc.) be reduced to as low a level as practicable in order to avoid poisoning the environment or catalysts such as steam reforming catalysts, water-gas shift catalysts, etc. Furthermore, fuel cell electrodes will rapidly become inactivated as the result of high levels of gaseous sulfur compounds in the fuel stream since the electrodes invariably contain precious metal components, e.g., platinum, which are extremely sensitive to the presence of sulfur compounds.
Also, removal of sulfur compounds from gas streams has been of considerable importance in the past and is even more so today due to environmental considerations. Gas effluent from the combustion of organic materials, such as coal, almost always contain sulfur compounds and sulfur removal processes have concentrated on removing hydrogen sulfide since it has been considered a significant health hazard and because it is corrosive, particularly when water is present. With increasing emphasis on eliminating or minimizing sulfur discharge to the atmosphere, attention is turning to removal of other sulfur compounds from gas streams.
Sulfur contaminants in natural gas streams include hydrogen sulfide, mercaptans, sulfides, and disulfides which due to their odorous nature can be detected at parts per million (ppm) concentration levels. Thus, it is desirable for residential and commercial users of natural gas to have concentrations of mercaptans lowered to 1 ppm and total concentrations of sulfur compounds to 20 ppm or less.
Numerous natural gas wells produce what is called in the industry as “sour gas.” “Sour gas” is natural gas that contains hydrogen sulfide, mercaptans, sulfides and disufides in concentrations that make its use unacceptable. Considerable effort has been expended to find an effective and cost efficient means to remove these objectionable sulfur compounds from natural gas.
Transmission companies that purchase natural gas from well owners and then distribute to consumers are very critical of sulfur content and require total sulfur content to be less than 30 ppm. Thus, owners of sour gas wells that exceed the 30 ppm limit are constantly searching for new and more efficient means to make their gas salable.
A number of processes are known for the removal of H2S from natural gas streams. Processes presently available can be categorized as those based on physical absorption, solid absorption or chemical reaction. Physical absorption processes suffer from the fact that they frequently encounter difficulty in reaching the low concentration of hydrogen sulfide required in the sweetened gas stream. Solid bed absorption processes suffer from the fact that they are generally restricted to low concentrations of H2S in the entering gas stream. Chemically reacting processes in general may be able to meet sweet gas specifications (primarily H2S concentrations), however, other reactions may occur with other material present in the gas stream. Above all, the processes presently available do not effectively provide for the removal of mercaptans, sulfides and disulfides.
While iron oxide has been used as an absorbent in the past, the surface area of these prior materials is significantly low such that large amounts of the absorbent need to be used and large amounts of the absorbent remain unexposed to the gas or liquid stream, after uptake at the surface of the absorbent has occurred. Thus, in the past, previous absorbents required large containers for efficient treatment to occur. This has been especially true for the treatment of sour gas.
Accordingly, there is a need to develop materials and methods to address or overcome one or more of the above-identified problems.